Effect Of Exogenous Sulfate On The Chromium(?)Metabolic Characteristics Of Chromium(?)-resistant Engineered Bacteria

Objective To construct chromium-resistant engineered bacteria by using ChrA and ChrB genes which related to chromium resistance in Serratia sp.S2,and explore the response mechanism of engineered bacteria to exogenous sulfate by studying the influence of different concentrations of sulfate on its chromium(VI)metabolism characteristics.Methods ChrA / ChrB / ChrAB engineered bacteria were constructed by genetic recombination technology,and evaluated the Cr(VI)resistance ability,growth curve,removal ability,absorptionand efflux of engineered bacteria under low,medium and high concentrations of sulfate;RT-qPCR was used to detect the transcription levels of Cr(VI)resistance-related genes(ChrA,ChrB)and sulfate channel protein-related genes(sbp,cysA,cysU,cysW)under different treatment conditions.The characristcs of chromium metabolism in engineered bacteria was analyzed under different concentrations of sulfate.Results PCR identification and protein expression indicated ChrA / ChrB / ChrAB engineered bacteria were successfully constructed.Cr(VI)resistance ability: sulfate can enhance the Cr(VI)tolerance ability of engineered bacteria,and the effect increased with the increasing of sulfate concentration(P < 0.05).Growth curve: sulfate has no effect on the growth of engineered bacteria in the absence of Cr(VI)(P > 0.05);with Cr(VI),the growth of engineered bacteria can be promoted by sulfate,and the promotion effect is enhanced with the increasing of sulfate concentration(P < 0.05).Cr(VI)removal ability: sulfate can enhance the Cr(VI)removal ability of engineered bacteria,and it increases continuously with the increasing of sulfate concentration(P < 0.05).Cr(VI)absorption: sulfate reduced the absorption of Cr(VI)in engineered bacteria with increasing sulfate concentration(P < 0.05).Cr(VI)efflux: sulfate inhibited the efflux of Cr(VI)in engineered bacteria with the increasing of sulfate concentration(P < 0.05).Transcription level of chrome-resistant genes(ChrA,ChrB): compared with the condition without Cr(VI),the transcription levels increased with the addition of Cr(VI)(P < 0.05);under the condition of Cr(VI),the transcription levels decreased successively with the increasing of sulfate concentration(P < 0.05).Transcription level of sulfate channel protein-related genes(sbp,cysA,cysU,cysW): compared with the condition without Cr(VI),the transcription level increased with Cr(VI)(P < 0.05).With or without Cr(VI),the transcriptional levels were decreased in order under the high and medium concentrations of sulfate(P < 0.05).At the same sulfate concentration,Cr(VI)tolerance capacity,removal capacity,and efflux were ChrAB strain > ChrA strain > ChrB strain(P < 0.05);Cr(VI)absorption was ChrB strain > ChrA strain > ChrAB strain(P < 0.05);transcription level of ChrA gene was ChrA strain > ChrAB strain(P < 0.05),and ChrB gene transcription level was ChrB strain > ChrAB strain(P < 0.05);transcription levels of sulfate channel protein-related genes(sbp,cysA,cysU,cysW)were ChrAB strain < ChrA strain ? ChrB strain.Conclusion Sulfate can inhibit Cr(VI)absorption and efflux of engineered bacteria in concentration-dependent manner through competitive action and down-regulation of relevant gene transcription levels,but when the interior of the bacteria reaches a dynamic equilibrium,the effect of sulfate on Cr(VI)absorption is greater than that of Cr(VI)efflux,resulting the Cr(VI)tolerance ability,growth ability and Cr(VI)removal ability of engineered bacteria were enhanced with the increasing of sulfate concentration.ChrAB engineered bacteria is more suitable for the actual Cr(VI)pollution environment.